Bipolar ion exchange membrane electrolytic cell

ABSTRACT

The present invention has an object of providing a bipolar type ion exchange electrolytic cell which is capable of minimizing the anode-cathode distance by a movable system which has a low electric resistance and which is simple and inexpensive, thereby to substantially reduce the electrolysis voltage. The present invention is a bipolar type ion exchange membrane electrolytic cell comprising an anode compartment frame which comprises an anode plate and an anode back plate arranged in substantially parallel with each other with a spacing, conductive anode supporting members arranged with a prescribed spacing from one another between the anode plate and the anode back plate, and a cathode compartment frame which comprises a cathode plate and a cathode back plate arranged in substantially parallel with each other with a spacing, and conductive cathode supporting members arranged with a prescribed spacing from one another between the cathode plate and the cathode back plate, so that the respective back plates are connected back to back to form a compartment frame unit, a plurality of such compartment frame units being arranged with a cation exchange membrane interposed, wherein at least the cathode supporting members comprise a flexible member, and the cathode plate is movably supported by the function of the flexible member.

TECHNICAL FIELD

The present invention relates to a bipolar type ion exchange membraneelectrolytic cell which is suitably useful for the production of e.g. anaqueous alkali metal hydroxide solution.

BACKGROUND ART

Heretofore, as an ion exchange membrane electrolytic cell to be used fore.g. production of an aqueous alkali metal hydroxide solution, a filterpress type electrolytic cell has been used in many cases. This is onewherein a number of ion exchange membranes and compartment frame unitseach comprising an anode compartment frame and a cathode compartmentframe, are alternately arranged and clamped from both sides by e.g. ahydraulic press. Types of electrolytic cells are generally classifiedinto a monopolar type electrolytic cell (monopolar cell) of a parallelconnection type and a bipolar type electrolytic cell (bipolar cell) of aseries connection type, which are distinguishable by the difference inelectrical connection.

As shown in FIGS. 1 and 2, in a compartment frame unit (general term foran anode compartment frame and a cathode compartment frame) for abipolar type electrolytic cell, an anode compartment 15 and a cathodecompartment 25 are arranged back to back, and an anode compartment frame10 constituting the anode compartment 15, comprises an anode plate 30and an anode back plate 40 arranged in substantially parallel with theanode plate with a spacing therefrom. As such an anode plate, it iscommon to employ a meshed or porous plate. For example, a conductivemeshed plate of e.g. titanium, zirconium or tantalum is used as asubstrate, and an oxide of a noble metal such as titanium oxide,ruthenium oxide or iridium oxide, is coated thereon.

Between the anode plate 30 and the anode back plate 40, corrosionresistant conductive anode supporting members (called also as ribs) 50 amade of e.g. titanium or a titanium alloy, are arranged with aprescribed spacing from one another to electrically connect the two andto maintain the spacing therebetween. Each anode supporting member 50 amay, for example, be made of a plate member and provided with aplurality of through-holes (not shown) so that an electrolyte can flowin the left and right directions in FIGS. 1 and 2.

The construction of the cathode compartment frame 20 for providing acathode compartment 25 is the same as that of the anode compartmentframe 10. Namely, it comprises a meshed or porous cathode plate 60, acathode back plate 70 and cathode supporting members 80 a.

Similarly, between the cathode plate 60 and the cathode back plate 70,corrosion resistant conductive cathode supporting members 80 a made ofe.g. iron, nickel or a nickel alloy, are arranged with a prescribedspacing from one another to electrically connect the two and to maintainthe spacing therebetween, as shown e.g. in FIG. 1.

The anode back plate 40 and the cathode back plate 70 are integrallyconnected to form a partition wall 9. Between the anode back plate 40and the cathode back plate 70 constituting the partition wall 9, aconductive interlayer member such as a cladding material (not shown) maybe inserted in order to increase the electrical conductivity. Aperipheral edge portion of each of the anode back plate 40 and thecathode back plate 70 constituting the partition wall, is bent and fixedto a hollow body 7 by e.g. welding. Reference numeral 11 indicates anion exchange membrane, and numeral 12 a gasket. The cathode plate ispreferably made of an alkali resistant material, such as a substratemade of e.g. a conductive meshed plate of e.g. nickel or stainlesssteel, coated with a cathode active material such as Raney nickel or aplatinum series.

In a case where such a bipolar cell is used for electrolysis of analkali metal halide such as sodium chloride to produce an alkali metalhydroxide, an almost saturated sodium chloride aqueous solution issupplied as an anolyte to an anode compartment from an anolyte inlet 3which is usually provided at a lower portion of the anode compartment.In the anode compartment, chlorine gas is generated on the anode plateby electrolysis, and it will be discharged, together with the aqueoussodium chloride solution as the electrolyte, out of the anodecompartment frame from an anolyte outlet 4 which is provided usually atan upper portion of the anode compartment.

On the other hand, in a cathode compartment, water or a dilute sodiumhydroxide aqueous solution is supplied as a catholyte to the cathodecompartment from a catholyte inlet 5 which is provided usually at alower portion of the cathode compartment. In the cathode compartment,hydrogen gas and sodium hydroxide are formed and discharged out of thecathode compartment from a catholyte outlet 6 which is provided at anupper portion of the cathode compartment.

The role of an ion exchange membrane used for this sodium chlorideelectrolysis, is to let sodium ions pass from the anode compartment sideto the cathode compartment side and to shut off movement of hydroxylions generated on the cathode side to the anode compartment side.

Usually the anode plate 30 is fixed to e.g. anode supporting members 50a in the anode compartment by e.g. welding. Likewise, the cathode plate60 is also fixed to e.g. cathode supporting members 80 a in the cathodecompartment by e.g. welding, and the anode plate 30 and the cathodeplate 60 are clamped with an ion exchange membrane interposed viagaskets 12 so that they maintain a prescribed distance. In general, thedistance between the anode plate and the cathode plate (theanode-cathode distance) is a factor giving a substantial influence overthe electrolysis voltage of the electrolytic cell. As a matter ofcourse, the shorter the anode-cathode distance, the lower theelectrolysis voltage, so that the electric power can be saved. On theother hand, if the anode and the cathode are too close to each other,the electrode plates are likely to contact with the membrane, since themembrane itself is flexible, and its position in the electrolyte is notcompletely fixed. In such a case, as numerous fine irregularities orprojections are present on the surface of the electrode plates, if themembrane moves in frictional contact with the electrode plate surface insuch a state that these irregularities or projections are forciblypressed against the membrane, the membrane is likely to be forcibly cut.

If a substantial portion of the membrane is thus damaged, normaloperation of the electrolytic cell tends to be finally impossible.Accordingly, heretofore, the operation is obliged to be carried out on asafe side by increasing the anode-cathode distance to such an extentwhere there will be no possibility of damaging the membrane, even if theelectrolysis voltage is sacrificed to some extent.

Some attempts have been proposed in the past not to give a damage to anion exchange membrane even if the membrane is disposed as close aspossible to an anode plate or a cathode plate having such fineirregularities or projections. For example, JP-A-57-108278 discloses atechnique wherein a number of conductive spring members are providedbetween an electrode plate and a partition plate on the anode sideand/or the cathode side to make the electrode plate movable. Further,JP-A-1-55392 discloses a technique wherein a partition plate and anelectrode plate are electrically connected by a clamp spring mechanism,and at the same time, the electrode plate is made movable by theresilience of the clamp spring mechanism.

These are techniques whereby even if the electrode plate and a membraneare in contact with each other, the pressing pressure can be reduced,but each employs a movable mechanism by springs, whereby there has beena problem such that (1) the electrical resistance at the spring memberportions increases, or (2) the production costs tend to increase becauseof the. complexity in the structure of the spring mechanism. (3) A moreserious problem is that since a movable mechanism whereby the spacingbetween the electrode and the partition wall is maintained solely by thespring members having resiliency, even if it is possible to make theelectrode plate movable, it is necessarily impossible from its mechanismto maintain the anode-cathode distance which must be uniformlymaintained over the entire electrolytic surface. Therefore, even if itis possible on appearance to reduce the anode-cathode distance by themovable mechanism, in reality, it is impossible to maintain theuniformity of the anode-cathode distance during a steady operation, andfrom the overall viewpoint, it has been impossible to effectively reducethe electrolysis voltage.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to solve such problems and toprovide a bipolar type ion exchange electrolytic cell which is capableof reducing the electrolysis voltage substantially by minimizing theanode-cathode distance by a simple and inexpensive movable mechanismhaving a low electrical resistance. Further, it is an object of thepresent invention to provide a bipolar type ion exchange electrolyticcell whereby even if the spacing between the electrode plate and the ionexchange membrane is made to be from 0.1 to 1.0 mm, there will be nodanger of damage to the membrane.

Firstly, the present invention provides the following invention.

A bipolar type ion exchange membrane electrolytic cell comprising ananode compartment frame which comprises an anode plate and an anode backplate arranged in substantially parallel with each other with a spacing,conductive anode supporting members arranged with a prescribed spacingfrom one another between the anode plate and the anode back plate, and acathode compartment frame which comprises a cathode plate and a cathodeback plate arranged in substantially parallel with each other with aspacing, and conductive cathode supporting members arranged with aprescribed spacing from one another between the cathode plate and thecathode back plate, so that the respective back plates are connectedback to back to form a compartment frame unit, a plurality of suchcompartment frame units being arranged with a cation exchange membraneinterposed, wherein

(a) at least the cathode supporting members comprise electric currentsupply rib base portions fixed to the cathode back plate and standing uptowards the cathode plate, and a flexible member supported by theadjacent electric current supply rib base portions and extending toreach the cathode plate,

(b) the flexible member and the cathode plate are electrically connectedto each other via a connecting portion of the flexible member, and

(c) electric current supply from the cathode plate to the electriccurrent supply rib base portions is carried out through the connectingportion, and the cathode plate is movably supported by the function ofthe flexible member.

Secondly, the present invention provides the following invention.

A bipolar type ion exchange membrane electrolytic cell comprising ananode compartment frame which comprises an anode plate and an anode backplate arranged in substantially parallel with each other with a spacing,conductive anode supporting members arranged with a prescribed spacingfrom one another between the anode plate and the anode back plate, and acathode compartment frame which comprises a cathode plate and a cathodeback plate arranged in substantially parallel with each other with aspacing, and conductive cathode supporting members arranged with aprescribed spacing from one another between the cathode plate and thecathode back plate, so that the respective back plates are connectedback to back to form a compartment frame unit, a plurality of suchcompartment frame units being arranged with a cation exchange membraneinterposed, wherein

(a) at least the anode supporting members comprise electric currentsupply rib base portions fixed to the anode back plate and standing uptowards the anode plate, and a flexible member supported by the adjacentelectric current supply rib base portions and extending to reach theanode plate,

(b) the flexible member and the anode plate are electrically connectedto each other via a connecting portion of the flexible member, and

(c) electric current supply from the electric current supply rib baseportions to the anode is carried out through the connecting portion, andthe anode plate is movably supported by the function of the flexiblemember.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of a compartment frame unit of a bipolar type ionexchange membrane electrolytic cell to carry out the present invention,as observed from a cathode compartment frame.

FIG. 2 is a view showing the cross section of the compartment frame unitalong line A—A in FIG. 1 together with ion exchange membranes andgaskets, and represents a conventional case having no movable mechanismin a cathode compartment.

FIG. 3 is a partially cross-sectional diagrammatical view of acompartment frame unit illustrating a typical embodiment of the presentinvention.

FIG. 4 is a partially cross-sectional diagrammatical view of acompartment frame unit illustrating a case wherein conductive platemetal chips and non-conductive spacers are provided.

FIG. 5 is a partially cross-sectional diagrammatical view of acompartment frame unit illustrating another embodiment of the presentinvention.

FIG. 6 is a partially cross-sectional diagrammatical view of acompartment frame unit illustrating another embodiment of the presentinvention.

EXPLANATIONS OF SYMBOLS

1 a lower portion of a compartment frame

2 an upper portion of the compartment frame

3 an anolyte inlet

4 an anolyte outlet

5 a catholyte inlet

6 a catholyte outlet

7 a hollow body

9 a partition wall for a bipolar electrolytic cell

10 an anode compartment frame

11 an ion exchange membrane

12 a gasket

15 an anode compartment

20 a cathode compartment frame

25 a cathode compartment

30 an anode plate

40 an anode back plate

50 a an anode supporting member (rib)

60 a cathode plate

70 a cathode back plate

80 a a cathode supporting member (rib)

90 a cathode back plate or a partition wall plate

95 a cathode plate

97 an anode

99 an anode back plate or a partition wall plate

100 a cation exchange membrane

101, 101′ an electric current supply rib base portion

102 a connecting portion (a supporting portion) of a flexible member andan electric current supply rib base portion

103, 103′ a flexible member or a flexible plate metal

105, 105′ a connecting portion on the flexible member

109, 109′ a protrusion of the flexible plate metal

110′ an anode supporting member (M type electric current supply rib) onthe anode side

113′ a shoulder portion of the M type electric current supply rib

120 a M type electric current supply rib on the cathode side

123 a shoulder portion of the M type electric current supply rib on thecathode side

130 a M type electric current supply rib on the anode side

133 a shoulder portion of the M type rib on the anode side

201 a spacer formed of a non-conductive material

205 a plate metal chip

p,p′ an apex of the protrusion

A1, A1′ the width of the flexible plate metal

A2, A2′ a spacing between the cathode plate and the portion of the platemetal other than the protrusion (the height of the protrusion)

A3, A3′ the height of the electric current supply rib base portion

A4 the width of the M type rib

A5 a spacing between the cathode plate and the fixed electric currentsupply rib base portion

Vd a closed space formed between the plate metal and the partition wallplate

Vu a space between the plate metal and the cathode plate

BEST MODE FOR CARRYING OUT THE INVENTION

Now, the present invention will be described in detail with reference tothe drawings.

The electrolytic cell to which the present invention is applicable, maybe of a monopolar type or a bipolar type. However, it is preferably abipolar type ion exchange membrane electrolytic cell and is basically abipolar type ion exchange membrane electrolytic cell comprising, asshown in FIG. 2, an anode compartment frame which comprises an anodeplate and an anode back plate arranged in substantially parallel witheach other with a spacing, conductive anode supporting members arrangedwith a prescribed spacing from one another between the anode plate andthe anode back plate, and a cathode compartment frame which comprises acathode plate and a cathode back plate arranged in substantiallyparallel with each other with a spacing, and conductive cathodesupporting members arranged with a prescribed spacing from one anotherbetween the cathode plate and the cathode back plate, so that therespective back plates are connected back to back to form a compartmentframe unit, a plurality of such compartment frame units being arrangedwith a cation exchange membrane interposed. And, as shown in FIG. 3, thebasic embodiment is such that (a) at least the cathode supportingmembers comprise electric current supply rib base portions 101 fixed tothe cathode back plate 90 and standing up towards the cathode plate 95,and a flexible member 103 supported by the adjacent electric currentsupply rib base portions 101 and extending to reach the cathode plate.Further, 102 indicates a connecting portion of the flexible member andthe electric current supply rib base portion, and this is also asupporting portion at which the flexible member is supported by theelectric current supply rib base portion.

And, (b) the flexible member extending to the cathode plate and thecathode plate are electrically connected to each other via a connectingportion 105 of the flexible member. (c) Through this connecting portion105, an electric current flows from the cathode plate 95 to the electriccurrent supply rib base portions 101, and the above connecting portionis also a mechanical connecting point for transmission of a force,whereby when an external force is exerted to the cathode plate, forexample, by generation of a gas in the cathode compartment, the aboveflexible member 103 may move for example, in a vertical direction to thecathode plate, with the connecting portion 105 as the starting point, sothat the cathode plate is displaced to protect the ion exchange membranefrom damage. Here, when the flexible member 103 moves, the supportingportions 102 and 102 will be fulcrums for the movement.

The present invention is thus characterized in that the cathodesupporting members comprise electric current supply rib base portionsfixed to the cathode back plate and standing up towards the cathodeplate, and a flexible member supported by the adjacent electric currentsupply rib base portions and extending to reach the cathode plate.

Namely, by this construction, the heights (A3) of base portions of thefixed electric current supply rib base portions are constant, whereby itis possible to protect the cation exchange membrane by changing theanode-cathode distance in the minimum range required not to damage themembrane by slightly displacing only the flexible member (the spacing A5between the cathode plate 95 and the fixed electric current supply ribbase portions 101) supported by this base portions depending upon thechange of the external force, while maintaining the anode-cathodedistance basically at a constant value.

The flexible member extends in its upper and lower directions to theupper and lower ends of the electrolysis area, and an appropriateclearance such as an opening or a cut edge is preferably provided at itsupper and lower ends.

A more specific embodiment of the flexible member of the presentinvention is shown in FIG. 3 wherein the flexible member 103 is made ofa flexible plate metal 103 having at least one protrusion 109 formedsubstantially at its center, and the apex p of this protrusionconstitutes the above-mentioned connecting portion 105.

The flexible plate metal 103 preferably has a plate thickness of from0.1 to 1.0 mm, its width A1 is from 4 to 25 cm, and the spacing A2between the cathode plate and the portion of the plate metal other thanthe protrusion 109 (in other words, the height of the protrusion) isfrom 3 to 30 mm. The flexible plate metal is selected from e.g.plate-shaped soft steel, stainless steel, nickel and nickel alloys, andcopper and copper alloys, and such a metal is used by processing it tohave the above-mentioned shape.

On the assumption that a flexible plate metal as such a flexible memberis installed in a cathode compartment in FIG. 1 showing a front view ofa compartment frame of a bipolar type ion exchange membrane electrolyticcell, as observed from a cathode compartment frame, in the presentinvention, cathode supporting members 80 a in the Figure correspond tothe electric current supply rib base portions 101, and the flexibleplate metal is supported by the adjacent electric current supply ribbase portions, respectively, i.e. it is installed between 80 a 1 and 80a 2, 80 a 2 and 80 a 3, 80 a 3 and 80 a 4, . . . , respectively. Namely,the flexible plate metal is installed to extend substantially over theentire area in the cathode compartment. The cathode plate 60 in theFigure is electrically and mechanically connected to this flexible platemetal, and the cathode plate is designed to be movable substantiallyuniformly in the direction of the anode plate (the rear side of thesheet surface) over the entire electrolysis area in the Figure. Namely,when the cathode plate is contacted to the cation exchange membranepresent on the front side of the sheet surface, the flexible plate metalwill move in the direction of the anode plate (on the rear side of thepaper sheet) by the pressing pressure to displace the cathode plate toreduce the pressing pressure, so that the membrane will not be damaged.Further, by permitting the flexible metal to have sufficient resiliency,the membrane may be strongly clamped between the cathode plate and theconventional fixed anode plate facing via a cation exchange membrane,whereby the membrane will be free from being damaged.

Thus, in the electrolytic cell of the present invention, the entire areaof the cathode plate can be brought uniformly close to the cationexchange membrane, whereby the anode-cathode distance can be shortened,and the electrolysis voltage can substantially be reduced.

As described in the foregoing, in a preferred embodiment of the presentinvention, the spacing between the cathode plate and the cation exchangemembrane can be set even in a very small range of from 0.1 to 2.0 mm,preferably from 0.1 to 1.0 mm.

In the present invention, the spacing between the cathode plate and thecation exchange membrane can be adjusted by changing the thickness ofthe gasket 12 installed along the periphery of the compartment frame orby changing the height A2 of the protrusion 109 of the plate metal.

The material for the flexible plate metal to be used in the presentinvention, can be selected by the formula (1).

δ(mm)=K×P(kg/cm²)  (1)

wherein δ is the movable degree (mm) of the flexible plate metal, K is aconstant determined by the material and the shape of the metal, and P isthe pressure (kg/cm²) exerted to the protrusion of the flexible platemetal.

Here, δ is the movable degree when the protrusion receives pressure P ofe.g. pressing pressure, more accurately, the movable degree within theresiliency, and with a flexible metal made of a prescribed metalmaterial and having a certain shape, on the basis of an assumedpressure, the movable degree under the pressure can be calculated. As amatter of course, one having a larger value of the constant K, forexample, one having higher softness and flexibility, is readily movablesimply when it receives a slight pressure P.

In the present invention, the movable degree of the cathode plate ispreferably at most 10 mm. Accordingly, the optimum value can bedetermined by carrying out simulation by means of the formula (1) byvariously changing factors such as (1) selection of the type of themetal material, (2) selection of the shape such as the plate thickness,the width A1 and the height A2 of the protrusion, so that the movabledegree of the flexible plate metal will be from 0 to 10 mm.

In the present invention, the value of K is preferably within a range offrom 0.2 to 200, more preferably within a range of from 4 to 40.

In the present invention, a non-conductive spacer may be interposedbetween the anode plate and the cation exchange membrane, so that thetwo will not be in direct contact with each other even when the spacingbetween the cathode plate and the membrane is very small. FIG. 4illustrates this state, wherein 201 represents a spacer formed of anon-conductive material.

As the spacer, basically any material may be employed so long as it isnon-conductive. However, preferably, it is a non-conductive resin orrubber (namely, an elastic body or an elastomer). Such a resin is notparticularly limited, and it is, for example, polypropylene orpolytetrafluoroethylene (PTFE), and the rubber may, for example, bebutyl rubber or an ethylene-propylene-diene rubber (EPDM). The resin orrubber may be a porous body or a foamed body. These may be used in asuitable form such as a plate-form, a sheet-form, a film-form, afiber-form or a spherical form. Spacers 201 of such a form are to bedisposed basically between the cathode plate and the cation exchangemembrane. More specifically, it is most preferred to dispose themrespectively above the apexes (the forward ends) p of protrusions of theflexible plate metal. However, they may be disposed, respectively,between protrusions. In either case, the spacers thus disposed, will beprovided above or in between the cathode supporting plates 80 a 1, 80 a2, 80 a 3, . . . which correspond to the electric current supply ribbase portions in FIG. 1. Further, the spacers are preferably disposedwith a proper spacing in the upper or lower direction of the compartmentframe and linearly provided.

The spacer may be one formed of e.g. a resin having a hardness of fromD40 to D80 (D scale test method according to ASTM D2240), or one formedof a rubber softer than the hardness of the membrane.

Here, spacers made of e.g. rubber are employed to prevent deformation ofthe membrane by creep. Namely, for example, when the cathode plate ispressed against the cation exchange membrane with non-conductive spacersinterposed therebetween, the two are not in direct contact with eachother by the presence of the spacers. However, if the operation iscarried out for a long period of time in a state where the pressingpressure is too strong, the membrane itself is likely to undergo creepdeformation due to the pressing pressure, and the polymer in theinterior of the membrane at the deformed portion is likely to undergochemical deterioration, and finally, pinholes may be formed in themembrane.

In such a case, if spacers made of non-conductive rubber or elastomersofter than the hardness of the membrane, are employed, even if theabove-mentioned pressing pressure results, the spacers themselves willserve as a cushion material and will suitably be deformed, so that thepressing pressure can readily be reduced, and the creep deformation ofthe membrane can effectively be prevented.

The thickness of the spacer is preferably from 0.1 to 1.0 mm. Whenspacers having a hardness of D40 to D80 are installed, the spacingbetween the ion exchange membrane and the cathode plate corresponding tothe thickness will be maintained even during the operation. Whereas,with spacers made of an elastic body softer than the hardness of themembrane, the distance between the membrane and the cathode plate can bemaintained with a spacing slightly thinner than the thickness of thespacer, during the operation.

Further, in the present invention, preferably, the connection betweenthe cathode plate 95 and the connecting portion 105 at the apex p of theprotrusion, is carried out via a plate metal chip 205 inserted and fixedi.e. interposed between the two.

This plate metal chip 205 is made of e.g. soft stainless steel, nickelor copper and fixed to the cathode plate and the connecting portion atthe apex of the protrusion by means of e.g. welding to protect theconnecting portion.

Namely, when the electrolytic cell is operated for a long period oftime, the cathode performance decreases, and it becomes necessary everya few year to dismount the cathode plate from the electrolytic cell andmount a fresh cathode plate. If the cathode plate and the apex of theprotrusion of the flexible plate metal are directly bonded by e.g.welding, the apex (the forward end portion) of the plate metal issusceptible to mechanical damage such as breakage or cracking from thisportion even with a small force, since it is shape-wise a weak portionparticularly in mechanical strength, during an operation to cut off thecathode plate from the flexible plate metal. In such a case, it becomesnecessary to replace the flexible plate metal itself. By interposing theplate metal chip between the cathode plate and the connecting portion atthe apex of the protrusion, the force exerted at the time of cutting offthe cathode plate from the flexible plate metal will be concentrateddirectly on the plate metal chip and will not be exerted to the apex ofthe plate metal, whereby there will be no substantial possibility thatthe apex of the protrusion of the flexible plate metal will receive adamage.

The thickness of the plate metal chip is preferably from 0.5 to 3.0 mm.Further, with respect to the width, it is preferred that one having awidth of from 3 to 15 mm is arranged in the up and down direction of thecompartment frame, and it has a length of at least ½ of the height inthe up and down direction of the compartment frame in consideration ofthe electric current distribution on the cathode plate.

FIG. 5 shows another embodiment of the present invention. Namely, thisis a case wherein an electric current supply rib base portion 101′ and aflexible member 103′ are integrally formed by e.g. mold processing.

More specifically, the electric current supply rib base portion 101′ andthe flexible plate metal 103′ are integrally formed in a cross-sectionalshape by e.g. mold processing, and this flexible plate metal 103′ iselectrically connected to the cathode back plate (partition plate) 90 bye.g. welding so that it forms a closed space together with the cathodeback plate.

This flexible plate metal 103′ is electrically and mechanicallyconnected to the cathode plate 95 with the apex p′ of a substantiallycenter protrusion 109′ constituting a connecting portion 105′, and ithas mobility similar to the plate member 103 shown in FIG. 3, and withthe protrusion 109′, the cathode plate 95 can be brought to besufficiently close to the cation exchange membrane without damaging themembrane.

In such integral formation, it is preferred that the portioncorresponding to the electric current supply rib base portion is formedto have a thicker cross section in order to increase the rigiditythereby to secure the fixing function, and the portion corresponding tothe flexible plate metal is made to have a thin plate thickness therebyto secure flexibility.

The thickness of this flexible plate metal, the width A1′ and thespacing (the height of protrusion) A2′ between the cathode plate and theplate metal, can be handled in the same manner as the numerical valuesfor the thickness of the flexible plate metal 103, the width A1 and thespacing A2 between the cathode plate and the plate metal, in FIG. 3.

In this embodiment, the plate metal 103′ may be made to havesimultaneously a downcomer function to promote the circulation of theelectrolyte in the compartment frame. Namely, an opening or a cut edgefor circulation of the electrolyte is provided at each of the upperportion and the lower portion of the compartment frame of the platemetal 103′, so that a closed space Vd formed between the plate metal103′ and the partition plate 90 constitutes a down flow pathway for thedown flow of the liquid. On the other hand, a space Vu between the platemetal 103′ and the cathode plate 95 constitutes an up flow pathway forthe liquid and gas. The two are connected via the above-mentionedopening or cut edge to form a continuous circulation flow pathway.

On the other hand, the corresponding anode side anode supporting member(electric current supply rib) 110′ has a cross section of M shape, andthe M-type electric current supply rib 110′ is electrically secured tothe anode back plate by e.g. welding so as to form a closed spacetogether with the anode back plate (partition plate) 99. Further, theM-type electric current supply rib 110 is fixed at both side shoulders113′ to the anode 97 by e.g. welding, to form an anode compartment.

FIG. 6 shows a still another embodiment of the present invention. Anelectric current supply rib 120 on the cathode side is one having across section of M shape, and this M-type electric current supply rib iselectrically fixed to the partition plate 90 by e.g. welding to form aclosed space together with the partition plate.

The flexible plate metal 103 is supported by adjacent electric currentsupply ribs. In such a case, it is fixed by e.g. welding at the opposingshoulders 123 of the adjacent M-type electric current supply ribs. Themanner in which the flexible plate metal 103 is electrically andmechanically connected to the cathode plate 95 via a connecting portion105 constituted by the apex p of the protrusion 109 at a substantiallycenter portion, is the same as described with respect to FIGS. 3 and 4.

Further, the thickness of this plate metal, the width A1 and the spacing(the height of the protrusion) A2 between the cathode plate and theplate metal, can be handled in the same manner as the numerical valuesfor the thickness of the flexible plate metal 103, the width A1 and thespacing A2 between the cathode plate and the plate metal, in FIG. 3.Further, the width A4 of the M-type electric current supply rib ispreferably from about 50 to 70 mm.

On the other hand, on the anode side, a similarly M-type electriccurrent supply rib 130 is disposed to face the electric current supplyrib 120 on the cathode side via a cation exchange membrane 100, and asalready described with respect to FIG. 5, the M-type electric currentsupply rib 130 is electrically fixed to the anode back plate 99 by e.g.welding so as to form a closed space together with the anode back plate(the partition plate), and further, the M-type electric current supplyrib 130 is fixed to the anode 97 by e.g. welding at the both sideshoulders 133, to form an anode compartment.

In the foregoing description, reference is made to a case wherein thecathode supporting members comprise electric current supply rib baseportions fixed to the cathode back plate and standing up towards thecathode plate, and a flexible member supported by the adjacent electriccurrent supply rib base portions and extending to reach the cathodeplate. However, as is readily understood, the anode supporting membersmay, of course, comprise electric current supply rib base portions fixedto the anode back plate and standing up towards the anode plate, and aflexible member supported by the adjacent electric current supply ribbase portions and extending to reach the anode plate. In such a case, inthe forgoing description, the cathode supporting members constituting aflexible member may be read as the anode supporting members, and thecathode plate to which the flexible member is to be connected, may beread as the anode plate. Therefore, detailed description will beomitted.

Now, the present invention will be described in further detail withreference to Examples, but the technical scope of the present inventionis by no means limited thereto.

EXAMPLE 1

Each of the anode and the cathode had a size such that the height was1200 mm, the width was 2400 mm and the effective electrolytic area was2.88 m². For the anode, DSE (an expanded mesh having a plate thicknessof 1.5 mm) manufactured by Permelek Electrode Co., Ltd., was used. Forthe cathode, a nickel expanded mesh having a plate thickness of 1.2 mmwas used as the substrate, and an activated Raney nickel alloy wascoated thereon. For the anode back plate, a plate made of titanium wasused, and for the cathode back plate, a plate made of nickel was used.These back plates were welded and bonded to each other to form thepartition plate.

For the electric current supply rib on the anode side, a titanium platehaving a thickness of 2.0 mm and a width of 35 mm was used. Eighteenelectric current supply ribs were welded and fixed to the back plate andthe anode with an equal spacing in the height direction of thecompartment frame, to form an anode compartment. Further, for theelectric current supply rib on the cathode side, a nickel plate having athickness of 1.0 mm and a width of 30 mm was used, and eighteen electriccurrent supply ribs were fixed to the back plate by welding with anequal spacing in the height direction of the compartment frame.

And, as shown in FIG. 3, as the flexible plate metal 103 having aprotrusion at the center, a nickel plate was employed which wasprocessed so that with the plate thickness of 0.5 mm, the width A1 was140 mm, the height A2 of the protrusion 109 was 10 mm, and the spacingA5 between the cathode plate 95 and the fixed electric current supplyrib base portions 101, was 4 mm. Both ends of this plate metal wereattached to the cathode electric current supply ribs by welding, and theapex p of the protrusion was attached as the connecting portion 105 tothe cathode plate likewise by welding, to form a cathode compartmentframe. Such compartment frame units comprising an anode compartment anda cathode compartment, and cation exchange membranes, are alternativelyarranged with a gasket 12 interposed, as shown in FIG. 2 and clampedfrom both sides by a clamping means made of iron so that the distancebetween the membrane and the cathode plate became 1 mm, and the movabledegree of the flexible plate metal was 2 mm at the maximum, to assemblea bipolar type ion exchange membrane electrolytic cell. Further, for theion exchange membranes, Flemion F893 (registered trademark of AsahiGlass Company, Limited) was used.

Into the anode compartments, an aqueous sodium chloride solution of 300g/l was supplied from a lower portion of the compartment frames, so thatthe sodium chloride concentration at the outlet became 210 g/l, and intothe cathode compartments, a dilute sodium hydroxide aqueous solution wassupplied from a lower portion of the compartment frames, so that theconcentration of the sodium hydroxide aqueous solution at the outletbecame 32 wt %.

Electrolysis tests were carried out at an electrolytic temperature of90° C. under a current density of 6 kA/m². As a result, the electrolysisvoltage was 3.25 V.

EXAMPLE 2

Each of the anode and the cathode had a size such that the height was1200 mm, the width was 2400 mm and the effective electrolytic area was2.88 m². For the anode, DSE (an expanded mesh having a plate thicknessof 1.5 mm) manufactured by Permelek Electrode Co., Ltd., was used. Forthe cathode, one having an activated Raney nickel alloy coated on anickel expanded mesh having a plate thickness of 1.2 mm, was used. Forthe anode back plate, a plate made of titanium was used, and for thecathode back plate, a plate made of nickel was used. These back plateswere bonded by welding to form a partition plate.

As shown in FIG. 5, on the cathode compartment side, a flexible platemetal 103′ made of nickel and having a protrusion at the center portionwas attached by welding to the cathode back plate 90 in the heightdirection of the compartment frame. 12 Plate metals 103′ each having athickness of 0.5 mm, a width A2′ of 160 mm, a spacing A2 between thecathode plate 95 and the plate metal 103′ being 10 mm and a height fromthe back plate 90 to the apex p′ of the protrusion being 40 mm, werearranged with equal spacing on the electrolysis area. The cathode platewas bonded and fixed to the plate metals 103′ by welding with the apexof the protrusion 109′ of each plate metal being a connecting portion105′.

A spacer 201′ formed of a PTFE resin and having a thickness of 0.5 mm, awidth of 10 mm and a length of 1150 mm, was disposed at a positioncorresponding to the apex p′ (i.e. the connecting portion 105′) of thisprotrusion, between the cation exchange membrane 100 and the cathodeplate 95.

On the other hand, on the anode compartment side, as shown in FIG. 5, atitanium electric current supply rib 110′ molded to have a M shape, wasattached to the anode back plate 99 by welding. This M-type electriccurrent supply rib 110′ was one which had a plate thickness of 2.0 mm, awidth of 160 mm and a height from the anode back plate 99 to the forwardends of the shoulder portions 113′ of the M-type electric current supplyrib being 35 mm, and it was welded and fixed to the anode plate 97 atthe forward ends of the shoulder portions.

Such compartment frame units each comprising an anode compartment and acathode compartment, and cation exchange membranes, are alternatelyarranged with gaskets 12 interposed, and clamped from both sides by aclamping means made of iron so that the movable degree of the flexibleplate metal became 2 mm at the maximum, to assemble a bipolar type ionexchange membrane electrolytic cell. The spacing between the membraneand the cathode plate was maintained to be 0.5 mm by spacers made ofPTFE. For the cation exchange membranes, Flemion F893 (registeredtrademark of Asahi Glass Company, Limited) was used.

Into the anode compartments, an aqueous sodium chloride solution of 300g/l was supplied from a lower portion of the compartment frames, so thatthe sodium chloride concentration at the outlet became about 210 g/l,and into the cathode compartments, a dilute sodium hydroxide aqueoussolution was supplied from a lower portion of the compartment frames, sothat the concentration of the sodium hydroxide aqueous solution at theoutlet became 32 wt %.

Electrolysis tests were carried out at an electrolytic temperature of90° C. under a current density of 6 kA/m². As a result, the electrolysisvoltage was 3.16 V, and the current efficiency was 96.3%. After theoperation for 150 days, the electrolytic cell was disassembled, wherebyno abnormality was observed.

EXAMPLE 3

The anode plate, the cathode plate and the partition structure were thesame as used in Example 1. In the cathode compartment, molded M-typeelectric current supply ribs 120 made of nickel were attached to theback plate by welding in the height direction of the compartment frame,as shown in FIG. 6. The M-type electric current supply ribs 120 used,were those having a plate thickness of 1.0 mm, a width A4 of 60 mm and adistance A3 from the back plate to the forward ends of the shoulderportions 123 being 30 mm, and 12 such ribs were disposed with an equalspacing in the electrolysis area. On the other hand, both ends of aflexible plate metal 103 were fixed, respectively, to the forward endsof the opposing shoulder portions 123 of the adjacent M-type electriccurrent supply ribs. As the flexible plate metal 103, the same one asused in Example 1, was employed, and the apex p of the protrusion 109was fixed and connected as a connecting portion 105 to the cathode plateby welding. Further, in the same manner as in Example 2, spacers 201were disposed between the membrane and the cathode plate. The spacersused, were the same 15 as used in Example 2.

Further, in the anode compartment, molded M-type electric current supplyribs 130 made of titanium were fixed to the back plate 99 by welding inthe height direction of the compartment frame so as to face the electriccurrent supply ribs 120 of the cathode. The M-type electric currentsupply ribs 130 used, were those having a plate thickness of 2.0 mm, awidth of 60 mm and a distance from the back plate to the forward ends ofthe shoulder portions 133 being 35 mm, and they were welded and fixed tothe anode plate 97 at the forward ends of such shoulder portions 133.

Compartment frame units each comprising such an anode compartment and acathode compartment, and cation exchange membranes, were alternatelyarranged with a gasket 12 interposed, and clamped from both sides by aclamping means made of iron so that the movable degree of the flexibleplate metal became 3 mm at the maximum, to assemble a bipolar type ionexchange membrane electrolytic cell. Further, the spacing between themembrane and the cathode plate was maintained to be 0.5 mm by PTFEspacers, in the same manner as in Example 2.

Into the anode compartments, an aqueous sodium chloride solution of 300g/l was supplied from a lower portion of the compartment frames, so thatthe sodium chloride concentration at the outlet became 210 g/l, and intothe cathode compartments, a dilute sodium hydroxide aqueous solution wassupplied from a lower portion of the compartment frames, so that theconcentration of the sodium hydroxide aqueous solution at the outletbecame 32 wt %.

Electrolysis tests were carried out at an electrolytic temperature of90° C. under a current density of 6 kA/m². As a result, the electrolysisvoltage was 3.16 V, and the current efficiency was 96.3%. After theoperation for 150 days, the electrolytic cell was disassembled, wherebyno abnormality was observed.

Comparative Example 1

An electrolytic cell was constructed in the same manner as in Example 1except that the cathode plate was attached directly to the cathode ribswithout using a flexible plate metal, and the spacing between themembrane and the cathode plate was changed to 2.5 mm. Using thiselectrolytic cell, electrolysis of sodium chloride was carried out underthe same conditions as in Example 1, whereby the electrolysis voltagewas 3.39 V, and the current efficiency was 96.2%.

INDUSTRIAL APPLICABILITY

According to the present invention, the cathode supporting members inthe cathode compartment are constituted by electric current supply ribbase portions and a flexible plate metal or the like supported by suchbase portions, whereby shortening of the distance between the anode andthe cathode has been realized by a safe and simple method, and it isthereby possible to substantially reduce the electrolysis voltage whileavoiding a danger of damage to the membrane.

According to the present invention, it is possible to provide a bipolartype ion exchange membrane electrolytic cell which can be operatedconstantly even at a high electrolytic current density of at least 4kA/m² and which provides a high current efficiency and a lowelectrolysis voltage which can effectively be applied for e.g.production of an aqueous alkali metal hydroxide solution.

What is claimed is:
 1. A bipolar ion exchange membrane electrolytic cellcomprising an anode compartment frame which comprises an anode plate andan anode back plate arranged substantially parallel with each other witha space therebetween, conductive anode supporting members arranged witha prescribed spacing from one another between the anode plate and theanode back plate, and a cathode compartment frame which comprises acathode plate and a cathode back plate arranged substantially parallelwith each other with a space therebetween, and conductive cathodesupporting members arranged with a prescribed spacing from one anotherbetween the cathode plate and the cathode back plate, so that therespective back plates are connected back to back to form a compartmentframe unit, a plurality of such compartment frame units being arrangedwith a cation exchange membrane interposed, wherein (a) at least thecathode supporting members comprise electric current supply rib baseportions fixed to the cathode back plate and extending up towards thecathode plate, and a flexible member supported by the adjacent electriccurrent supply rib base portions and extending to reach the cathodeplate, wherein the electric current supply rib base portions, flexiblemember, and cathode back plate define a closed space which does notcontain the cathode plate, (b) the flexible member and the cathode plateare electrically connected to each other via a connecting portion of theflexible member, and (c) electric current supply from the cathode plateto the electric current supply rib base portions is carried out throughthe connecting portion, and the cathode plate is movably supported bythe function of the flexible member.
 2. The bipolar ion exchangemembrane electrolytic cell according to claim 1, wherein the flexiblemember is made of a flexible plate metal, at least one protrusion isformed at substantially the center thereof, and the apex of theprotrusion constitutes the connecting portion.
 3. The bipolar ionexchange membrane electrolytic cell according to claim 2, wherein theflexible plate metal has a thickness of from 0.1 to 1.0 mm and a widthof from 4 to 25 cm, and the spacing between the cathode plate and aportion of the plate metal other than the protrusion is from 3 to 30 mm.4. The bipolar ion exchange membrane electrolytic cell according toclaim 2, wherein the connection between the cathode plate and theconnecting portion at the apex of the protrusion is carried out via aplate metal chip inserted between the two.
 5. The bipolar ion exchangemembrane electrolytic cell of claim 4, wherein the plate metal chipcomprises a metal selected from the group consisting of soft stainlesssteel, nickel, and copper.
 6. The bipolar ion exchange membraneelectrolytic cell of claim 4, wherein the plate metal chip has athickness of 0.5 to 3.0 mm, and a width of 3 to 15 mm.
 7. The bipolarion exchange membrane electrolytic cell according to claim 2, whereinthe movable degree of the cathode plate is at most 10 mm.
 8. The bipolarion exchange membrane electrolytic cell according to claim 2, whereinthe elastic force of the flexible plate metal is represented by theformula (1) and K is within a range of from 0.2 to 200:δ(mm)=K×P(kg/cm²)  (1) where δ is the movable degree (mm) of theflexible plate metal, K is a constant determined by the material and theshape of the metal, and P is the pressure (kg/cm²) exerted to theprotrusion of the flexible plate metal.
 9. The bipolar ion exchangemembrane electrolytic cell according to claim 2, wherein anon-conductive spacer is disposed between the cathode plate and thecation exchange membrane, so that the cathode plate and the cationexchange membrane do not contact directly each other.
 10. The bipolarion exchange membrane electrolytic cell according to claim 9, whereinthe spacer has a hardness of from D40 to D80 (D scale test methodaccording to ASTM D2240).
 11. The bipolar ion exchange membraneelectrolytic cell of claim 9, wherein the non-conductive spacercomprises a non-conductive resin, a non-conductive rubber, or anon-conductive elastomer.
 12. The bipolar ion exchange membraneelectrolytic cell of claim 11, wherein the non-conductive spacer isporous or foamed.
 13. The bipolar ion exchange membrane electrolyticcell of claim 11, wherein the non-conductive spacer comprises a materialselected from the group consisting of polytetrafluoroethylene, butylrubber, and ethylene-propylene-diene rubber.
 14. The bipolar type ionexchange membrane electrolytic cell according to claim 2, wherein thespacing between the cathode plate and the cation exchange membrane isfrom 0.1 to 1.0 mm.
 15. The bipolar ion exchange membrane electrolyticcell according to claim 1, wherein the spacing between the cathode plateand the cation exchange membrane is from 0.1 to 1.0 mm.
 16. The bipolarion exchange membrane electrolytic cell of claim 1, wherein the flexiblemember is a metal selected from the group consisting of soft steel,stainless steel, nickel, nickel alloys, copper, and copper alloys. 17.The bipolar ion exchange membrane electrolytic cell of claim 1, whereinthe flexible members extend substantially over the entire area of thecathode compartment.
 18. A bipolar ion exchange membrane electrolyticcell comprising an anode compartment frame which comprises an anodeplate and an anode back plate arranged substantially parallel with eachother with a space therebetween, conductive anode supporting membersarranged with a prescribed spacing from one another between the anodeplate and the anode back plate, and a cathode compartment frame whichcomprises a cathode plate and a cathode back plate arrangedsubstantially parallel with each other with a space therebetween, andconductive cathode supporting members arranged with a prescribed spacingfrom one another between the cathode plate and the cathode back plate,so that the respective back plates are connected back to back to form acompartment frame unit, a plurality of such compartment frame unitsbeing arranged with a cation exchange membrane interposed, wherein (a)at least the anode supporting members comprise electric current supplyrib base portions fixed to the anode back plate and extending up towardsthe anode plate, and a flexible member supported by the adjacentelectric current supply rib base portions and extending to reach theanode plate wherein the electric current supply rib base portions,flexible member, and anode back plate define a closed space which doesnot contain the cathode plate, (b) the flexible member and the anodeplate are electrically connected to each other via a connecting portionof the flexible member, and (c) electric current supply from theelectric current supply rib base portions to the anode is carried outthrough the connecting portion, and the anode plate is movably supportedby the function of the flexible member.